The present invention relates generally to control systems for liquid dispensers and, more particularly, to a control system and method for controlling the dispensed liquid spray pattern of a liquid dispensing system.
Various liquid dispensing systems have been developed to dispense a liquid spray pattern from a nozzle outlet toward a surface of a substrate. For example, in conformal coating applications, liquid dispensing systems have been designed to dispense flat, fan-like liquid spray patterns of conformal coating material onto a surface of the substrate, such as a printed circuit board. The dispensing nozzle of these systems may be a cross-cut, slit or air-assisted slot nozzle, for example, that is configured to dispense the coating material as a spray, continuous band or sheet, or fibrous web of a predetermined pattern width toward the circuit board. The dispensing nozzle is typically moved by a robotic movement platform in opposite back-and-forth directions relative to the circuit board to dispense side-by-side tracks or bands of conformal coating onto the circuit board and thereby obtain a uniform moisture resistant barrier on the board surface. Alternatively, the circuit board may be moved relative to the liquid dispenser which may be fixed.
During the conformal coating process, it is important that the tracks or bands of coating join or converge along their adjacent edges, or even slightly overlap, to ensure that a full surface coating is provided on the board. Otherwise, the circuit board will be left vulnerable to undesirable chemical or moisture attack by any gaps left between the coating tracks or bands. On the other hand, too much overlap of the adjacent edges may cause undesirable bubbles in the thickened coating areas at the overlap that may also jeopardize quality control. Thus, a consistent width of the liquid spray pattern is generally necessary to obtain a uniform layer of conformal coating on circuit boards.
Unfortunately, while a liquid material dispenser may adequately and reliably dispense uniform conformal coating layers on circuit boards in one production run, changes in the viscosity and/or fluid pressure of the material will often lead to undesirable variations in the liquid spray pattern width. Additionally, contamination or partial blockage of the nozzle outlet will cause the spray pattern to become offset relative to a centerline of the nozzle. When this occurs, one edge of the liquid spray pattern is spaced from the nozzle outlet centerline a greater distance than the other edge. If these changes are not detected prior to a production run, improperly coated boards must be reworked and costly downtime of the conformal coating system is typically required to identify the problem and manually adjust the liquid dispensing system to obtain the desired pattern width and minimal offset. As those skilled in the art will readily appreciate, pattern width control is also critical in other liquid dispensing applications as well, such as in paint, flux and hot melt adhesive dispensing environments. In each of these applications, very often the edge positions of the dispensed liquid pattern relative to a substrate surface or to an adjacent liquid pattern dispensed on the substrate must be properly adjusted and set to obtain the desired material application.
Thus, there is a need for a control system for use in a liquid dispensing system that improves width control of the dispensed liquid spray pattern.
There is also a need for a control system for use in a liquid dispensing system that improves the operator""s ability to readily identify problems in the dispensed liquid spray pattern.
There is yet also a need for a control system for use in a liquid dispensing system that improves the operator""s ability to adjust the width of the liquid spray pattern to accommodate for variations in liquid material viscosities and pressures.
The present invention overcomes the foregoing and other shortcomings and drawbacks of liquid dispenser control systems and methods heretofore known. While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. On the contrary, the invention includes all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention.
The control system of the present invention is operable to measure and adjust the liquid spray pattern dispensed from a liquid dispensing system. In one embodiment of the present invention the control system includes a sensor fixture located in the vicinity of the liquid dispensing system, and an interface unit that is electrically and fluidly connected to the sensor fixture. The interface unit is also fluidly connected to the liquid dispensing system and a source of supply air, and further electrically coupled to a robot controller of an X-Y-Z robot movement platform associated with the liquid dispensing system.
The sensor fixture includes a drain pan or receptacle for receiving and draining liquid material that is dispensed from the liquid dispensing system during a pattern measurement and adjustment procedure. The drain pan is fluidly connected to a fluid reservoir that is connected to main system vent air. A pair of fiber optic sensors are mounted in confronting relationship on opposite sides of the drain pan. Each of the sensors is mounted in a sensor shroud that is releasably engageable with the drain pan through one of a pair of upstanding resilient fingers or clips formed on opposite side walls of the drain pan. The sensor shrouds each receive regulated supply air from the interface unit so that air flows toward the dispensed liquid spray pattern to keep the sensors free from contamination during the measurement and adjustment procedure.
The interface unit of the control system includes a voltage/pressure regulator that is operable to provide a regulated output air pressure to a pneumatically controlled fluid regulator associated with the liquid dispensing system. The regulated output air pressure supplied by the voltage/pressure regulator is controlled by a pressure controller of the interface unit. The pressure controller is operable to receive signals from the robot controller to increase or decrease the regulated output air pressure supplied from the voltage/pressure regulator to the pneumatically controlled fluid regulator of the liquid dispensing system. The robot controller is operable to receive signals from a fiber optic amplifier of the interface unit that is electrically coupled to the pair of fiber optic sensors. The width of the liquid spray pattern dispensed from a nozzle of the liquid dispensing system may be readily varied by varying the output air pressure supplied from the voltage/pressure regulator to the pneumatically controlled regulator of the liquid dispensing system.
During a liquid spray pattern measurement or adjustment procedure, the sensors of the sensor fixture are operable to detect the presence or absence of an edge of the dispensed liquid spray pattern. In accordance with one aspect of the present invention, the nozzle of the liquid dispensing system is moved to a predetermined position relative to the sensors. The pattern width of the liquid spray pattern is automatically adjusted to the pattern width set by the operator by increasing or decreasing the width of the dispensed spray pattern until the presence or absence of an edge of the spray pattern is detected by the sensors.
In accordance with another aspect of the present invention, the nozzle is moved relative to the sensors until the opposite edges of the spray pattern are detected by the sensors. The positional location of each edge is recorded at the location of detection by the sensors. The control system is operable to measure the width of the dispensed spray pattern from the positional locations of the detected opposite edges of the spray pattern. If the measured pattern width falls outside of an acceptable range, a warning is provided to the operator. The control system is also operable to measure the offset of the spray pattern relative to a centerline of the nozzle from the positional locations of the detected edges of the spray pattern. If the measured offset falls outside of an acceptable range, a warning is also provided to the operator.
The above and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof.